1. Field of the Invention
The invention relates to an electric heating device for heating air which is in particular suited to be employed as additional electric heating in motor vehicles.
2. Description of the Related Art
For the employment in motor vehicles, in particular those with engines of which the consumption is optimized, electric heating devices are used to heat the passenger compartment andor the engine. An additional electric heating is in particular required after the starting of the engine as long as the internal combustion engine does not yet provide sufficient thermal energy. Internal combustion engines of which the consumption is optimized even principally require the use of an additional electric heating.
However, the use of such heating devices is not restricted to the field of motor vehicles; they are also suited for a plurality of other applications, for example in the field of domestic installations (room air conditioning), industrial plants and the like.
An electric heating device for motor vehicles is known from EP-A1-1 395 098. The described heating device comprises several heating elements assembled to a heating block. The heating block is held in a common frame together with a control means for controlling the heating elements. The control means thus forms a constructional unit together with the heating block held in the frame. The control means comprises power electronics with electronic switches which are provided each with a heat sink. The control means is arranged such that a portion of the air flow to be heated flows against the control means, in particular the cooler elements for cooling the electronic switches.
The electronic switches, in particular in the form of power transistors which control the current that is supplied to the heating elements, are mounted directly on a printed circuit board with one side. To dissipate the thermal loss generated by the power transistors, a cooler element is provided on the opposite side of the printed circuit board. Such a cooler element which directly contacts the power transistor can dissipate the thermal loss of the power transistor in a simple manner and in a sufficient amount.
In the above-mentioned prior art, a U-shaped heat sink with cooling fins or fingers, respectively, which project from a base, is employed. A pin is provided at the bottom side of the heat sink and can be inserted in the printed circuit board to contact the power transistor. However, a cooler element in the sense of the present invention can be any component which is suited to dissipate heat from the power transistors by heat conduction and emit it effectively to the air flowing around it by heat transfer. To this end, the cooler element is exposed to the air which is to be heated by the electric heating device, i.e. which flows in a channel leading to the electric heating device. However, it cannot be excluded that moisture collects in the channel which is either directly introduced with the inflowing air or is condensed from the air that has flowed in.